This invention relates to the separation of particles from beverage liquids, and in one embodiment to concentrating microorganisms (such as yeast and bacteria) in a sample of orange juice for sterility testing purposes, and in another embodiment to removing microorganisms, including for example, bacteria, any other particles from beverage liquids to eliminate the need for pasteurization.
In the past, the separation of particles from liquids has been accomplished by inertial separation methods or by some form of filtration. In the case of inertial separators, separation performance depends on the difference between the centrifugal and drag forces that act on the challenged particles. For such separators, the operator has little or no control over the separation process. In the case of filtration, separation is achieved by fluid passing through a semi-permeable medium capable of retaining on the medium, particles larger than the pore size of the medium.
Regardless of whether inertial separation or filtration is selected, the process becomes impractical as the particle size decreases and as the difference in density between the fluid and the particles decreases. Low density difference between particle and fluid eliminates inertial separators from contention, and particle sizes approaching that of the pore size of the medium cause serious loss of filter capacity.
In filtration, fluids can flow through filter media in two ways--normally or tangentially. In normal flow (see FIG. 4A), fluid passes perpendicular to the surface of the media, whereas in tangential flow (also know as cross flow--see FIG. 4B) fluid passes essentially parallel to the filter surface.
In many critical applications, normal flow filtration is completely useless, because the particles not passing through the filter medium remain close to or on top of the upstream surface of the medium. These particles form a layer that severely limits and eventually stops the fluid flow. In tangential flow filtration, on the other hand, the process flow moves tangentially to the filter surface, and it is hoped that the retained particles get swept along with the flow. As a result, a higher through-put is expected. Nevertheless, a "dead zone" forms adjacent to the static surface when fluid flows tangentially to it. At this dead zone the flow rate is zero, which results in particle stagnation. This pitfall renders tangential flow filtration unsuitable on industrial process equipment and limits it to laboratory use.
Two articles describing prior art devices are:
1. Burdyn, R. R., D E. Hawk & F. D. Patchen, "A New Device for Field Recovery of Barite: II Scale-Up and Design " Society of Petroleum Engineering Journal, June, 1965, and
2. Margaritis, A. and C. R. Wilke, "Engineering Analysis of the Rotorfermentor," Work performed under the auspices of the U.S. Atomic
Energy Commission, University of California, Berkeley, 1970.